The Kuydusun (Russian: Куйдусун; Yakut: Куйдуһун, Kuyduhun) is a river in Sakha Republic (Yakutia), Russia.

[1] The river flows south of the Arctic Circle, across desolate tundra territories of the Oymyakonsky District marked by permafrost.

Kuydusun village is located by the banks of the lower course of the river and Tomtor further north, near its mouth.

The river flows roughly in a northern direction across the mountainous territory, then turns northeastwards into a plain of the Yana-Oymyakon Highlands filled with lakes where it meanders and divides into multiple channels.

Finally the Kuydusun joins the left bank of the Indigirka 1,674 km (1,040 mi) from its mouth.